The position of an aircraft can be controlled through the use of one or more variable incidence control surface members. By moving these control surface members, changes in aircraft position can be induced, and unwanted aircraft positions can be corrected.
Typically, to reduce pilot workload, the incidence of the control surface member can be adjusted by an actuating device, which can be controlled automatically in dependence on a control signal issued by a signal processor on the basis of input parameters such as aircraft position, aircraft acceleration, airspeed, pilot stick inputs, etc., to control the aircraft position as desired.
For obvious reasons, the aircraft control surface member actuator must not be permitted to react to temporary deviations, but it must readily respond to gradual changes, in the input signal values, as sensed by the input sensors. To achieve such conditions, it has been proposed to subject the signal that are subject to such relatively rapid deviations to a low-pass filtering action.
In a typical implementation of this approach, a relatively large-capacity capacitor is connected in parallel with an operational amplifier that is arranged between the output of the sensor or sensors in question and the signal processor and which is charged, on the one hand, by the incoming unfiltered sensor signal issued by the sensor or sensors and, on the other hand, by the amplified sensor signal appearing at the output of the operational amplifier. A control arrangement of this type operates well and accomplishes its intended purpose so long as the supply of electric energy to the electrical system and particularly to the operational amplifier is uninterrupted. However, when using this control arrangement type, the capacitor is relatively quickly discharged, usually through the operational amplifier, if the electric power supply is interrupted. This means that, when the supply of the electric power is restored following such interruption, the signal supplied to the actuator that positions the aircraft control surface member may be incorrect in the sense that it will not have the value it would have had were it not for the interruption, in all cases except where the signal to the actuator was at a value corresponding to the value when the capacitor was discharged before the power interruption. This, in turn, means that an output signal which appears at the juncture of the output of the operational amplifier with the corresponding terminal of the capacitor and which controls, usually in conjunction with other parameters, the actuator that positions the aircraft control surface member, may cause the latter to adjust the this control surface member to an incorrect position, even though the input signal supplied by the input sensor or sensors may call for a different position of the aircraft control surface member. This undesirable condition will prevail until the capacitor is charged to such a level that the output signal supplied to the actuator has a value corresponding to the instantaneous position of the aircraft control surface member that it positions, whereupon the direction of movement of the aircraft control surface member is reversed by the actuator in response to further charging of the capacitor and corresponding increase in the value of the aforementioned output signal.
It is obvious that the above-described situation can have undesirable effects in the control of the aircraft, in that the control functions of the aircraft control surface member may be impaired for a period following the restoration of the electric power.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to develop an arrangement for controlling the position of an aircraft control surface member, which arrangement does not possess the disadvantages of the known arrangements of this type.
Still another object of the present invention is so to construct the arrangement of the type here under consideration as to be able to automatically recognize the restoration of the electric power supply following interruption and to modify the position of the aircraft control surface member in response to such recognition in such a manner as to avoid the incorrect position of the aircraft control surface member.
It is yet another object of the present invention to design the above arrangement in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
A concomitant object of the present invention is to provide an arrangement for controlling the operation of an actuator which adjusts the position of a movable member in such a manner that a temporary interruption of electric power supply will result only in a negligible, if any, change in the position of the movable member, regardless of the duration of the interruption.